Accelerometers are devices that provide an electrical signal output related to an acceleration level to which the accelerometer is subjected. Accelerometers are useful for numerous applications such as inertial navigation where continuous readings related to instantaneous acceleration are required.
Many types of accelerometers are known in the prior art; however, many prior art accelerometers suffer from one or more problems. They may be bulky, expensive, and/or may require elaborate support circuitry to provide their output signals.
While many accelerometer applications require an ongoing acceleration level from their associated accelerometers, other applications detect when a predetermined acceleration threshold has been reached. Such applications also may be satisfied by acceleration or shock-sensing switches that trigger (i.e., open, close, or otherwise signal) that a predetermined shock has occurred or an acceleration level has been reached.
A well-known example of a threshold detecting accelerometer relates to deploying motor vehicle air bags during a collision. While instantaneous acceleration levels of the vehicle may be useful for applications unrelated to air bag deployment, for that particular application only detection of an exceeded acceleration value due to external acceleration (i.e., not due to external forces or pressures), is required. Heretofore, elaborate systems have been required for detecting the acceleration and then deploying one or more air bags. Such systems generally require an accelerometer, amplification and/or other processing circuitry, a comparator circuit, and finally a switch to actually deploy the air bags. Such systems are relatively expensive and typically require many support components. This provides unnecessary opportunities for component failure resulting in less than optimally reliable systems.